Electrostatic electron lenses with telescopically adjustable tubular elements



Jan. 16, 1968 M. R. BENNETT 3,364,372-

ELECTROSTATIC ELECTRON LENSES WITH TELESCOPICALLY ADJUSTABLE TUBULARELEMENTS Filed July 30, 1964 mil-Jinnah:

INVENTOE WWMM United States Patent 3,364,372 ELECTROSTATIC ELECTRONLENSES WITH TELESCOPICALLY ADJUSTABLE TUBULAR ELEMENTS "Maurice RonaldBennett, Rayleigh, Essex, England, assignor to English Electric ValveCompany Limited,

London, England, a British company Filed July 30, 1964, Ser. No. 386,172Claims priority, application Great Britain, Aug. 14, 1963, 32,121/ 63 4Claims. (Cl. 313-85) The invention relates to electrostatic electronlenses and has particular application in cathode ray tubes.

Electrostatic lenses usedin cathode ray tubes generally comprises anEinzel lens, two types of which are shown in section in FIGURES 1 and 2respectively of the accompanying drawings. The lens shown in FIG. 1comprises two metal tubular electrodes 1 and 2 of the same diametercoaxially spaced a distance a apart. A third tubular metal electrode 3coaxially surrounds the gap between the electrodes 1 and 2 and extends alittle way over each of those electrodes. The three electrodes aresupported in their mutual relationship within the neck of the cathoderay tube (not shown) by wire supports attached to the electrodes, someof the supports being shown at 4. The wire supports are fused into glasssupport rods distributed around the structure, one of the rods beingshown at 5.

FIGURE 2 shows a different form of Einzel lens in which there are threeco-axial tubular electrodes 7, 8 and 9 of which 7, which is nearest thecathode end 10 of the lens, is of smallest diameter and 9, which isnearest the anode end 11 of the lens is of largest diameter. Theelectrode 8 is of intermediate diameter and overlaps electrode 7 and isoverlapped by electrode 9. Again the interrelationship of the electrodesis maintained Within the cathode ray tube by wire supports 12 fused intoglass rods of which one is shown at 13. In some tubes the largestdiameter electrode (3 in FIG. 1; 9 in FIG. 2) is constituted by aconductive coating on the inside of the neck of the cathode ray tube inwhich case, of course, this particular electrode has no separatesupport.

The distance [2 between the anode end of electrode 7 and the anode endof electrode 8 in FIG. 2, like the distance a in FIGURE 1, is ofparticular and critical importance in governing the performance of thelens. These distances have to be carefully pro-determined (in most casesto a value in the neighbourhood of half an inch) and a departure of aslittle as one thousandth of an inch from the predetermined value canresult in a substantial alteration of the focal length of the lens. Itis therefore of great importance that in the manufacture of the lensesthe distances a and b be closely controlled.

In the course of present-day normal manufacture the lens electrodes withtheir support wires attached are supported in their intended mutualrelationship in a jig and the ends of Wires are immersed in molten glassrods which are then allowed to set to hold the electrodes in place. Thisobviously involves subjecting the lens structure to large temperaturefluctuations so that expansion and contraction of the metal electrodesand glass rods renders the precise control of spacing of the electrodesvery difiicult.

The present invention seeks to avoid such ditliculty and render theprecise control of the more critical spacings of the lenses easierduring manufacture.

According to this invention at least one of the tubular electrodes of anelectron lens comprising a number of overlapping tubular electrodes isof telescopic construction whereby, after assembly and mounting of thelens electrodes the telescopically constructed electrode or electrodescan be finely adjusted as to the overall length thereof thereby toprovide with precision a desired inter-electrode relationship.

Preferably, after adjustment, the relatively movable parts of atelescopically constructed electrode are fixed in relation to oneanother by spot welding. The heat required to do this is normallyinsufiicient materially to upset the adjustment.

According to a feature of this invention a method of making an electronlens comprising co-axial overlapping tubular electrodes of which atleast one is of telescopic construction includes the steps of mountingthe electrodes by means including support wires fused into glass orlikesupport members, adjusting to a desired overall length thetelescopically constructed electrode after the electrodes have beenassembled and mounted and then fixing the adjustment made.

The invention not only gives the great advantage of attainment ofaccurate effective spacing without disturbance by heat processes used inmanufacture but also errors in inter-electrode spacing brought about byfailure to have the support wires in precisely the right positions canbe substantially eradicated by adjusting the telescopic electrode (orelectrodes: more than one can be telescopic) with fine accuracy and thenspot-welding or otherwise fixing the telescoping parts when adjustmentis complete.

The simplest form of telescopically constructed electrode for use incarrying out this invention consists of two parts one of which can beslid over the other.

A preferred form of Einzel lens in accordance with this invention andfor use in a cathode ray tube comprises three tubular electrodesrespectively of three different diameters that at the cathode end beingthe smallest and that at the anode end the largest and the smallestelectrode is of telescopic construction consisting of two parts of whichthe one nearer the cathode end is fixedly supported and the other,nearer the anode end can be adjusted towards or away from the nextlarger diameter electrode. Preferably the largest diameter electrode isconstituted by a conductive coating on the inside of the neck of thecathode ray tube.

One embodiment of the invention is illustrated in and explained inconnection with FIGURES 3 and 4 of the accompanying drawings, FIGURE 3showing an Einzel lens and FIGURE 4 showing a jig for making the lens ofFIGURE 3. The provision of a conductive coating on the interior of theneck wall of a cathode ray tube to constitute the electrode of largestdiameter is shown in FIG- URE 5.

FIGURE 3 shows an Einzel lens of the type described with reference toFIGURE 2 and the same reference numerals are used for all correspondingparts of the two figures. In the arrangement of FIGURE 3, however, thedistance from the anode end of electrode 7 to the anode end of electrode8 is made deliberately longer than the ultimately required distance amaking the part 7 shorter than it would be in a comparable known lens.In the part 7 is a slidable tubular stainless steel insert 14 which ineffect forms part of the electrode and. when the parts 7, 8 and 9 havebeen assembled and mounted, and have cooled the projection of the insert14 from the anode end of part 7 is adjusted to result in the requiredvalue for the distance 11 as measured from the anode end of insert 14 tothe anode end of electrode 8. The insert is then spot welded to the part7. A weld is indicated at 15.

An electrode 25 may be coated on the interior of the neck wall portion26 as illustrated in FIGURE 5 and the electrode 25 may, of course,correspond to the electrode 9 of largest diameter as shown in FIGURE 3.

FIGURE 4 shows a jig suitable for use in assembling the lens structureof FIGURE 3. Corresponding reference numerals are used for the lensstructure as in FIGURES 2 and 3. The jig comprises a support plate 16having a hole through which is passed a thread ended rod 17. At the endremote from the thread 18 the rod terminates in an enlarged end 19. Asleeve 20 of the same external diameter as the end 19 is mounted on therod 17 and between the end of the sleeve and a step presented by end 19is mounted a rubber collar 21. Tightening a wing 22 threaded on thread13 axially compresses and radially expands the rubber collar 21. Acylindrical block 23 is mounted on the plate 16 and closely surroundsthe sleeve 20. A metal collar 24- of accurately known length is asliding fit on sleeve 20 and abuts against the fiat end of block 23.

When the assembled structure comprising parts 7, 8 and 9 mounted bywires 12 fused in rods 13 has cooled the insert 14, which is dimensionedto be a sliding fit in part 7, is pushed into it to project from theanode end thereof. The assembly is then mounted on the jig in the mannershown in FIGURE 4 with the insert over the projecting end of the sleeve20. With the insert abutting against the end of the collar 24 the wingnut 22 is tightened so that the insert 14 is gripped internally by theexpanded rubber collar 21. This allows the insert to be held againsttwisting if the rest of the assembly is twisted relative to the jig soas to facilitate adjustment of the axial position of the insert in theassembly. By axial movement (which may be facilitated by twisting) theassembly is mounted on the jig so that the anode end of electrode 8abuts against the flat end of block 23. Since the anode end of insert 14abuts against the end of collar 24, the distance b corresponds to thelength of the collar 24 which is accurately determined. When in thisposition the electrode 14 is spot welded at 15 and other points to theelectrode 7. The Wing nut 22 is slackened and the assembled structurewithdrawn.

It will be seen that use of a different length collar 24 will give adifferent spacing b so that a whole range of electron lenses ofdifferent focal lengths may be produced by the insertion of inserts todifferent extents in a single type of basic lens structure. All that isrequired is a suit able range of collars 2 4.

The following remarks provide a practical illustration of theimprovement effected by the use of the invention in measuring thefocussing tolerance of a lens until the focal length is brought to thedesign value. In tests carried out on a batch of lenses made inaccordance with the invention 90% came within a focussing tolerance of:50 v. A comparable figure for tubes not made in accordance with theinvention is less than 90% with a tolerance of greater than :100 v. Thusan ancillary advantage of the invention is that the range of bias builtinto, say, a television set to compensate for tube focussing divergencemay be significantly reduced.

I claim:

1. An Einzel electron lens Comprising a plurality of assembled andmounted separated overlapping tubular lens electrodes of varyingdiameters and mounting means for supporting said electrodes in coarsepredetermined inter-electrode relationship, one of said electrodes beingdisposed in precisely determined inter-electrode spatial relationshipwith at least one further of said electrodes, said at least one furtherelectrode including two contacting tubular parts in telescopicrelationship and having a precisely fixed over-all length finelyadjusted subsequently to the mounting of the electrodes on said mountingmeans to provide said precisely determined inter-electrode spatialrelationship.

2. An electron lens as claimed in claim 1 wherein said tubularelectrodes comprise three overlapping electrodes of different diameters,said at least one further electrode having the smallest diameter.

3. An electron lens as claimed in claim 1 wherein another of saidtubular electrodes comprises a conductively coated inner surface of acathode ray tube.

4. A cathode ray tube having an envelope comprising an inner wall and anEinzel focussing lens comprising a plurality of assembled and mountedtubular electrodes of different diameters, one of said electrodes beingof largest diameter and comprising a conductive coating on said innerwall, mounting means for supporting the remaining electrodes in coarsepredetermined electrode spatial rela* tionship, one of said plurality ofelectrodes being disposed in precisely determined inter-electrodespatial relationship with at least one further of said plurality ofelectrodes, said at least one further of said electrodes including-twocontacting tubular parts in telescopic relationship and having aprecisely fixed over-all length adjusted subsequently to the mounting ofthe electrodes on said mounting means to provide said preciselydetermined inter-elem trode spatial relationship.

References Cited UNITED STATES PATENTS 2,174,853 10/1939 Bowie 3l3--85 X2,567,674 9/1951 Linder 3l384 X 2,720,606 10/1955 Dornfeld 31385 X2,935,642 5/1960 Schwartz 315-15 2,942,128 6/1960 Johnson 313-85 X3,082,342 5/1963 Pietri 315-15 X FOREIGN PATENTS 968,869 4/1958 Germany.

ROBERT SEGAL, Primary Examiner.

JAMES W. LAWRENCE, Examiner.

1. AN EINZEL ELECTRON LENS COMPRISING A PLURALITY OF ASSEMBLED ANDMOUNTED SEPARATED OVERLAPPING TUBULAR LENS ELECTRODE OF VARYINGDIAMETERS AND MOUNTING MEANS FOR SUPPORTING SAID ELECTRODES IN COARSEPREDETERMINED INTER-ELECTRODE RELATIONSHIP, ONE OF SAID ELECTRODES BEINGDISPOSED IN PRECISELY DETERMINED INTER-ELECTRODE SPATIAL RELATIONSHIPWITH AT LEAST ONE FURTHER OF SAID ELECTRODES, SAID AT LEAST ONE FURTHERELECTRODE INCLUDING TWO CONTACTING TUBULAR PARTS IN TELESCOPICRELATIONSHIP AND HAVING A PRECISELY FIXED OVER-ALL LENGTH FINELYADJUSTED SUBSEQUENTLY TO THE MOUNTING OF THE ELECTRODES ON SAID MOUNTINGMEANS TO PROVIDE SAID PRECISELY DETERMINED INTER-ELECTRODE SPATIALRELATIONSHIP.